2170 SSSAJ: Volume 73: Number 6 • November–December 2009 NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS A Contribution of the University of Nebraska Agricultural Research, Lincoln, NE 68583. Soil Sci. Soc. Am. J. 73:2170-2176 doi:10.2136/sssaj2007.0373 Received 15 Oct. 2007. *Corresponding Author (mmamo3@unl.edu). © Soil Science Society of America 677 S. Segoe Rd. Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. L ow soil fertility, particularly N and P defciencies, has long been recognized as a major constraint to crop production in sub-Saharan Africa (Nye and Greenland, 1960). Negative nutrient balances have repeatedly been demonstrated for this region (Goldman and Heldenbrand, 2003; Smaling et al., 1997; Wortmann and Kaizzi, 1998). Stoorvogel and Smaling (1990) estimated that about 200 million ha of cropland in Africa lost 600, 75, and 450 kg ha -1 N, P, and K, respectively, over a 30-yr period. Sanchez et al. (1997) wrote that soil fertility depletion is the fundamental biophysical cause of declining per capita food production in Africa. Little fertilizer is used due to inadequate supply, unstable commodity prices, scarce fnancial resources, and lack of credit availability (Kayuki and Wortmann, 2001). Soil P sorption and desorption dynamics are important to P availability and applied P recovery. Tropical soils can be grouped into four major categories in this regard with important impli- cations for P management. Volcanic soils contain allophane and have a high P sorption capacity that results in low P availability for crop production. Studies in Ethiopia showed good correlation between soil Al and the P sorption capacity of these volcanic ash soils (Tekalign and Haque, 1987). Another important category of agricultural soils in sub-Saharan Africa includes soils that have oxidic properties where sorption capacity is mainly determined by Fe and Al hydrous oxides coated clay particles (Frossard et al., 1995). Dufera and Robarge (1999) and Tekalign and Haque (1987) have shown that soil Fe and Al were major controlling factors of P sorption on soils of Ethiopia. Much of the P sorbed by Fe and Al compounds in these oxidic soils is slowly desorbed to the soil solution resulting in >50% recovery rates for applied P over a period of 5 to 10 yr (Sanchez et al., 1997). Calcareous soils form another category, where P is retained by precipitation with calcium carbonate to form apatite. Dissolution of P from apatite is very slow for basic soils with very low P recovery rates. Te fourth category includes sandy soils with limited sorption ca- pacity. Phosphorus retention by soil is an asset in P management with the sorbed P considered to be soil P capital for an estimated 530 million ha (Buresh et al., 1997; Gladwin et al., 2003). Te sorbed P is a capital if the P retention is reversible, and can slowly supply P to plants and reduce leaching losses, especially on more sandy soils. Termites modify soil physical, chemical, and biochemical properties and play a major role in nutrient cycling of tropical ecosystems (Lee and Wood, 1971; Salick et al., 1983; Holt and Coventry, 1990). Studies in tropical deserts have shown that termites might be responsible for up 20% of the organic mat- ter (OM) decomposition (Holt and Coventry, 1990). In dry tropical Africa, termites may represent up to 65% of the soil Martha Mamo* Charles Wortmann Dep. of Agronomy and Horticulture Univ. of Nebraska Lincoln, NE 68583 Phosphorus Sorption as Affected by Soil Properties and Termite Activity in Eastern and Southern Africa Phosphorus is ofen the limiting nutrient to crop production in eastern Africa. Efcient management of P requires an understanding of the factors afecting availability of soil native P and applied fertilizer P. Te objectives of this study were (i) to evaluate the relationships between soil properties and P sorption characteristics, and (ii) to assess the efect of termite activities on soil properties and P sorption characteristics. Phosphorus sorption isotherms were determined for 36 soils, including 7 samples from termite mounds and surrounding non-termite soils from Uganda and Mozambique. Ammonium-oxalate extractable Al (Al ox ) was the most important property explaining over 90% of the variation in P sorption maximum (S max ) for Uganda and Mozambique soils. However, for the Ethiopia soils 88% of the variation was explained by Mehlich-3 extractable Ca, ammonium-oxalate extractable P (P ox ), and sand content. Te S max of Uganda and Mozambique soils increased by 44 to 390% due to increased clay content from termite activities. Te higher S max of termite mounds implies a greater demand for P fertilizer for low P soils but also a higher P storage capacity and reduced risk of P leaching. Termite mound could be considered as a potential soil amendment. Abbreviations: Al ox , ammonium-oxalate extractable aluminum; CCE, calcium carbonate equivalent; Fe ox , ammonium-oxalate extractable iron; MBC, maximum bufer capacity; OM, organic matter; P ox , ammonium-oxalate extractable phosphorus; S max, phosphorus maximum sorption capacity. Published November, 2009